Magnetic resonance imaging (MRI) is a major imaging technique used in medicine. MRI is capable of generating detailed images of soft tissues such as the brain, muscles and kidneys. Specific properties of the various compounds found inside tissues, such as water and/or fat, are used to generate images. When subjected to a strong magnetic field, the vector sum of the nuclear magnetic moments of a large number of atoms possessing a nuclear spin angular momentum, such as hydrogen, which is abundant in water and fat, will produce a net magnetic moment in alignment with the externally applied field. The resultant net magnetic moment can furthermore precess with a well-defined frequency that is proportional to the applied magnetic field. After excitation by radio frequency pulses, the net magnetization will generate a signal that can be detected.
Delta relaxation enhanced magnetic resonance imaging (DREMR) generally referred to as field-cycled relaxometry or field-cycled imaging is an MRI technique that offers the possibility of using underlying tissue contrast mechanism which vary with the strength of the applied magnetic field to generate novel image contrasts. To achieve DREMR contrast, the main magnetic field is varied as a function of time during specific portions of an MR pulse sequence. A field-shifting electromagnet coil is used to perform the field variation. To date the DREMR imaging methods have focused on the effect of main magnetic field variations on the T1 relaxation characteristic of materials being imaged. This, however, is a limited use of a DREMR system.